This project investigates the potential of a sperm antigen, ph-20, as an immunocontraceptive in male and female macaques. Ph-20 was first isolated from guinea pig sperm by Dr. Paul primakoff at the university of connecticut, and he has now isolated cynomolgus ph-20 and produced rabbit antibodies to cph-20. This subproject is the major mating trial of ph-20 immunized female cynomolgus macaques. Thirty-two females have been monitored for urinary steroids to verify that ovarian cycles are normal. Currently, the final urine collections are being performed and the main study should begin within 2 months. These animals will be divided into 4 groups control and 3 levels of ph-20 immunization. Prior to injection, blood, cervical mucus and vaginal washes will be collected from all animals. Initial immunizations and 2 boosts with ph-20 and the adjuvant, titermax will be performed and if serum titers indicate good antibody response then mating trials will begin. Before mating trials begin, post-immunization samples of reproductive tract fluids will be collected. Each female will be mated three times per cycle at about the time of ovulation, as determined prior to injection by the urinary steroid assays, with a proven-fertile male (a different male each month) for 6 months. If treated females are not pregnant at the end of the mating trial, additional samples of reproductive tract fluids will be collected and ovarian function will be monitored by urinary steroids.